In the configuration of a related light-dimming device it has been known to adjust the light output of a lighting load (for example, see JP 2013-149498 A, hereinafter referred to as “Document 1”).
The light-dimming device disclosed in Document 1 includes a pair of terminals, a control circuit, a control power supply for supplying control power to the control circuit, and a light output adjuster for adjusting a light output level of the lighting load.
The control circuit and the control power supply are connected in parallel to each other between the pair of terminals. The pair of terminals allows a series circuit of an AC power supply and the lighting load to be connected between. The lighting load includes a plurality of LED (light emitting diode) elements and a power supply circuit for lighting the LED elements. The power supply circuit includes a smoothing circuit composed of a diode and an electrolytic capacitor.
The control circuit includes a switch for phase control of an AC voltage supplied to the lighting load, a switch driver for driving the switch, and a controller for controlling the switch driver and the control power supply.
The control power supply is connected in parallel to the switch. The control power supply converts the AC voltage of the AC power supply to the control power. The control power supply includes an electrolytic capacitor charged by the control power.
The controller is supplied with the control power from the control power supply through the electrolytic capacitor. The controller includes a microcomputer. The microcomputer performs reverse phase control of interrupting power supply to the lighting load during each half cycle of the AC voltage in accordance with a light output level adjusted with the light output adjuster.
As a related light-dimming device of this sort, a two-wire anti-phase control device has been proposed (for example, see JP 2011-238353 A, hereinafter referred to as “Document 2”).
The two-wire anti-phase control device disclosed in Document 2 includes a main current switching circuit, a dimming variable pulse delay circuit, and a DC power generation circuit.
The main current switching circuit includes a main current circuit and two MOSFETs connected in anti-series. The two MOSFETs are allowed to be connected in parallel to a series circuit of an AC power supply and a lighting load. The dimming variable pulse delay circuit is configured to determine discharge timing of a gate-charge of each of the MOSFETs. The DC power generation circuit is composed of an integration circuit of a resistor and a capacitor. The DC power generation circuit is configured to supply the dimming variable pulse delay circuit with a voltage across the capacitor as DC power.
The microcomputer of the controller in the light-dimming device disclosed in Document 1 performs the reverse phase control for the lighting load. In the light-dimming device, the switch conducts (turns on) from an OFF state when an absolute value of the AC voltage from the AC power supply is a value other than zero, and the electrolytic capacitor of the control power supply is charged by the control power for a certain period of time within time from the OFF state to turn-on of the switch. In the two-wire anti-phase control device disclosed in Document 2, the capacitor of the DC power generation circuit is charged over a period of time until each MOSFET is turned on from an OFF state.
However, in the light-dimming device of Document 1, when the series circuit of the AC power supply and the lighting load is connected between the pair of terminals, the lighting load is provided with the smoothing circuit and therefore the electrolytic capacitor may not be charged well by the control power. Because there is a possibility that when the switch is in an OFF state, a current would not flow through the lighting load depending on a conduction angle of the switch. This may cause unstable control operation of the controller with respect to the switch driver, thereby making it difficult to maintain a lighting state of the lighting load.